We propose to continue our studies of the influence of flow upon plasma protein interactions at interfaces, and their subsequent influence upon a) surface activation of clotting, b) adhesion of platelets and c) adhesion of granulocytes. Because of unexpected results obtained in recent months, we plan to pay special attention to narrow spaces, on surfaces that tend to activate the intrinsic clotting system. These results show that, while in wide spaces the plasma will deposit fibrinogen and will then replace it with the "surface factors" (high molecular weight kininogen and factor XII), in spaces of less than 10 microns the plasma will contain enough fibrinogen to deposit a film, but will lack the amount of surface factors needed to displace the fibrinogen. In blood, where platelets adhere to the fibrinogen film, more will adhere therefore in narrow spaces, especially where the erythrocytes act as a diluent of the plasma. Flow over rough surfaces will be studied in view of these findings.